1. Field of Invention
The invention relates to an automatic transmission mounted in a vehicle. In particular, the invention relates to a hydraulic control apparatus which controls the friction element in the transmission mechanism.
2. Description of Related Art
In order to control an automatic transmission for a vehicle, a hydraulic circuit controls the clutch and the brake (referred to as friction elements). The hydraulic circuit uses a specialty control valve (linear solenoid valve or duty solenoid valve) for each hydraulic servo (i.e., servo mechanism) of each friction element while independently controlling each valve. The control valves in the hydraulic circuit are permanently open to output hydraulic pressure in order to maintain certain running capabilities for the vehicle by outputting hydraulic pressure to the hydraulic servo even when signals to the control valves fail. Hence, if all of the control valves experience signal failure or stick failure simultaneously, the friction elements become engaged simultaneously. In order to avoid such a condition, Japanese patent publication No. 2689421, proposes a method in which a predetermined forward speed is achieved even when the control valves continue to output hydraulic pressure due to electrical failure or stick failure during the forward movement of the vehicle.
In the hydraulic circuit, the predetermined forward speed is established when the failure occurs while the vehicle is moving forward. However, if the vehicle is stopped and the engine is turned off after a failure occurs, for example, and the engine is turned on once again with the transmission shifted to drive (hereafter xe2x80x9cduring an engine restart timexe2x80x9d), or the transmission is shifted to drive after shifting to neutral or park, or if a condition occurs in which all of the released friction elements now supply hydraulic pressure to all of the friction elements, the predetermined forward speed remains.
A higher predetermined forward speed is preferred so that a driver does not experience an unexpected downshift feeling when a failure occurs during actual driving. However, when a vehicle is stopped and restarted after a failure during running, a lower vehicle speed is preferred because a certain amount of driving power is needed in restarting. If the achieved speed is only one speed, like in the aforementioned hydraulic circuit, an awkward predetermined forward speed must be established, which neither eliminates the downshift feeling nor secures the driving power due to the two contradicting requirements described above.
Hence, the invention provides a hydraulic control apparatus which establishes at least two speeds to satisfy the two aforementioned requirements, the elimination of the downshift feeling caused by a failure during driving and securing a sufficient amount of driving power to restart the vehicle after the occurrence of a failure.
In a first exemplary aspect of a hydraulic control apparatus, the hydraulic control apparatus comprises a hydraulic source (51), a first, a second and a third hydraulic paths (L32, L31, L5) which are connected to the hydraulic source (51), a first, a second and a third hydraulic servos (82, 81, 83, 84) which are connected with the first, second and third hydraulic paths (L32, L31, L5) and which operate a first, a second and a third friction elements (C-2, C-1, C-3, B-1) wherein predetermined forward speeds out of a plurality of speeds are achieved by engagement of at least two friction elements, a first, a second and a third control means (72, 71, 73, 74) which are arranged in the first, second, and third hydraulic paths (L32, L31, L5) and operate an engagement release through a supply and removal of hydraulic pressure to the first, second and third servos (82, 81, 83, 84) wherein, in the predetermined forward speeds, the first friction element (C-2) and the third friction element (c-3, B-1) are engaged by the first and third control means (72, 73, 74), a first valve (55) which is arranged in the second hydraulic path (L31) and which cuts off hydraulic pressure from the hydraulic source (51) to the second hydraulic servo (81) with downstream side hydraulic pressure, as a signal pressure, from at least the first control means (72); and a second valve (60) which is arranged in the first hydraulic path (L32) and which cuts off hydraulic pressure to the first hydraulic servo (82) and the signal pressure, wherein the downstream side hydraulic pressure of the first control means (72) and the downstream side hydraulic pressure of the third control means (73, 74) can be impressed as signal pressures to the first valve (55), the first valve (55) cuts off the hydraulic pressure from the hydraulic source (51) to the second hydraulic servo (81) when both of the signal pressures are impressed.
In the above-described composition, installation of the second valve (60) enables the supply of hydraulic pressure to the second hydraulic servo (81) when a position is assumed wherein hydraulic pressure to the first hydraulic servo (82) and a signal pressure to the first valve (55) are cut off However, the supply of hydraulic pressure to the second hydraulic servo is cut off, though the supply of hydraulic pressure to the first hydraulic servo is enabled, when the position to not cut off is assumed. Hence, engagement of various friction elements is enabled due to the position of the second valve, this achieving the least two forward speeds.
In other exemplary aspects, the hydraulic control apparatus further comprises, a third valve (53) arranged in between the hydraulic source (51) and the first and second control means (72, 71) and which is capable of selectively switching the supply and cutting off of hydraulic pressure to the first and second control means (72, 71), wherein, the second valve (60) assumes a position to cut off hydraulic pressure to the first hydraulic servo (82) and the signal pressure to the first valve (55) when the third valve (53) assumes a position to cut off hydraulic pressure to the first and second control means (72, 71).
In the above-described composition, by making the second valve (60) cut off the hydraulic pressure to the first hydraulic servo (82) and signal pressure to the first valve (55), when the third valve (53) assumes the position to cut off hydraulic pressure to the first and the second control means (72, 71), supply of hydraulic pressure to the first hydraulic servo (82) and the signal pressure to the first valve (55) are cut off even when the third valve (53) later assumes the position to supply hydraulic pressure to the first and the second control means (72, 71), enabling separate formation of forward speed, which makes it possible to set the different forward speed during operation of driving again by re-starting the engine from the condition in which the first and the second friction elements (C-2, C-1) are both released.
In other exemplary aspects, the second valve (60) is arranged in an upstream side of a signal pressure supply hydraulic path (L32), a branch of the first hydraulic path, to the first valve (55). Thus cutting off of hydraulic pressure to the first hydraulic servo (82) and the signal pressure to the first valve (55) may be achieved by one valve, which allows the size of the apparatus to be reduced.
In other exemplary aspects, the control apparatus is structured such that wherein when the first control means (32) outputs hydraulic pressure and a condition changes from engagement of the first friction element (C-2) to the second control means (71) ready to output hydraulic pressure, enabling supply of hydraulic pressure to the second hydraulic servo (81), at least predetermined forward speeds (5, 6 speed) are achieved by releasing the second friction element (C-1) using at least the first valve (55), and when the predetermined forward speed is high speed, the first friction element is released at a low speed and is engaged at a high speed, and the second friction element (C-1) which is released by hydraulic pressure to the first friction element (C-2) is engaged at low speeds (1, 2, 3 speed) and is released at high speeds.
In the above-described composition, if the supply of hydraulic pressure to the hydraulic servo, which operates the second friction element (C-1), is enabled due to occurrence of a failure during driving with the first friction element (C-2) of the vehicle engaged, high speed is achieved due to the release of the second friction element (C-1) which is engaged at low speed by hydraulic pressure to the first friction element (C-2) which is engaged at high speed, hence unnecessary down shift is prevented. Moreover, during re-starting of the vehicle after failure during running, supply of hydraulic pressure to hydraulic servo of the second friction element (C-1) which is engaged at low speed is enabled due to the cutting off of hydraulic pressure for the hydraulic servo of the second friction element (C-1) which is engaged at high speed to be applied to the first valve (55). Moreover, hydraulic pressure to the hydraulic servo of the first friction element (C-2) which is engaged at high speed is also cut off, establishing low speed without fail and assuring the driving power during re-starting of the vehicle.
In other exemplary aspects, the control apparatus comprises a signal pressure generation means for selectively switching the second valve (60) to the hydraulic pressure supply or cut-off positions to the first hydraulic servo (82), wherein the signal pressure generation means is a solenoid valve (75), capable of generating hydraulic pressure through electrical operation, and the solenoid valve (75) switches, when there is no electric current, the position of the second valve (60) to the position of cutting off hydraulic pressure to the first hydraulic servo (82).
In the above-described composition, supply or cut-off of hydraulic pressure to the hydraulic servo which operates the friction element may be selectively executed with a compact structure, enabling reduction in the size of the hydraulic control apparatus.
In other exemplary aspects, the second valve (60) is structured such that a spring force is given from one side and a signal pressure from the signal pressure generation means is applied from the other side, and the signal pressure generation means switches, by cutting off hydraulic pressure when there is no electric current, the position of the second valve (60) to the position of cutting off hydraulic pressure to the first hydraulic servo (82) by the spring force.
In the above-described composition, stabilization of the entire hydraulic control apparatus against hydraulic pressure is achieved by switching a position to cut off supply of hydraulic pressure to the first friction element (C-2) by spring force after cutting off hydraulic pressure when electric current is stopped, unlike a case in which switching of a position to cut off supply of hydraulic pressure to the friction element by supplying hydraulic pressure against spring force during the time of stopping current.
In other exemplary aspects, the control apparatus further comprises the third friction element (B-1) which is released with the first friction element (C-2) during the low speed (3 speed) time and the third hydraulic servo (84) which operates the third friction element (B-1), and a fourth valve (58) which switches with hydraulic pressure, as signal pressure, to a hydraulic servo (83) which operates a fourth friction element (C-3) for engaging hydraulic pressure supply or cut-off state time the third hydraulic servo during the low speed (3 speed) time. Thus, the low speed is achieved and driving force during re-starting is secured.
In other exemplary aspects, the low speed comprises a first forward speed, a second forward speed with the speeds consecutively increasing. Thus, even during the low speed, the third forward speed, a high speed, is achieved and power is secured, enabling near normal driving.
In other exemplary aspects, the control apparatus further comprises a fifth valve (56, 57) for switching hydraulic pressure supply or cut-off to the hydraulic servo (83) which operates the fourth friction element (C-3) to be engaged during the time of the third forward speed (3 speed) with hydraulic pressure, as signal pressure, to the second hydraulic servo (81, 84) which operates fiction elements to be engaged during the time of the predetermined forward speed (4, 6 speed), and hydraulic pressure to the first hydraulic servo (82) which is operated by the signal pressure generation means, is applied, as signal pressure, to the fifth valve (56, 57).
Moreover, in a vehicle where the fourth friction element (C-3) which engages during the third forward speed (3 speed) is released by the friction elements (C-1, B-1)which engages during the predetermined forward speed (4, 6 speed), early supply of hydraulic pressure to the hydraulic servo (81, 84) which operates the friction element which engages during the predetermined forward speed causes release of hydraulic pressure for the hydraulic servo (83), to be applied to the fourth valve (58), which operates the fourth friction element (C-3), which makes it impossible to achieve the third forward speed. However, hydraulic pressure for the hydraulic servo (82) which operates the first friction element (C-2) to be switched by the signal pressure generation means is applied to the fifth valve (56, 57), hence the fifth valve stop operation, enabling supply of hydraulic pressure to be applied to the fourth valve (58), and the third forward speed (3 speed) is achieved without fail.
In other exemplary aspects, the control apparatus further comprises a sixth valve (57) for switching hydraulic pressure supply or cut-off to the hydraulic servo (83) which operates the fourth friction element (C-3) to be engaged during the third forward speed (3 speed) with hydraulic pressure, as signal pressure, to the hydraulic servo (84) which operates the friction element (B-1) to be engaged during the time of predetermined forward speed (2, 6 speed), and the sixth valve (57) comprises a delay means (77) which delays hydraulic pressure supply speed to the hydraulic servo (84) which operates the friction element (B-1) to be applied to the sixth valve (57).
In the case of cutting off the supply of hydraulic pressure to the hydraulic servo (84), which operates friction element (B-1) in order to release, as signal pressure, the hydraulic pressure to the hydraulic servo (83) which operates the fourth friction element (C-3) which engages during the third forward speed, if the hydraulic pressure, as signal pressure, to the hydraulic servo (83) which operates the fourth friction element (C-3) functions as signal pressure from the hydraulic servo (84) which operates other friction element (B-1) during other forward speed (2, 6 speed) to cut off supply of hydraulic pressure, early supply of hydraulic pressure from the hydraulic servo (84) which operates other friction element cuts off the supply of hydraulic pressure to the hydraulic servo (83) which operates the fourth friction element. Hence, signal pressure to cut off friction element (B-1) which should be cut off to achieve the third forward speed is not applied, making it impossible to achieve the third forward speed. However, a delay means is provided to assure cutting off of the friction element without fail by the signal pressure to the fourth friction element (C-3).
In various other exemplary aspects, the predetermined forward speed is the second forward speed (3 speed), the friction element to be released with the first friction element (C-2) during the time of the second forward speed is the fourth friction element (C-3) to be engaged during the third forward speed (3 speed) time, and the friction element to be engaged during the second forward speed (2 speed) time is the third friction element (B-1) to be released during the third forward speed (3 speed) time.
In the above-described composition, the second forward speed is secured even if a failure occurs during driving with the second forward speed. Hence, unnecessary speed change is prevented even during driving with the second speed, eliminating uncomfortable feeling for a driver. Furthermore, by providing a delay means, the friction element is cut off without fail by a signal pressure of the fourth friction element (C-3).
In various other exemplary aspects, the second valve (60) is structured in such a manner that the hydraulic pressure to the hydraulic servo (82), which operates the friction element (C-2) to be released during the low speed (1, 2, 3 speed) time, is applied to the second valve (60), and the hydraulic pressure supply state is enabled by running current to the signal pressure generation means (75) when the friction element (C-2) is engaged, after which the hydraulic pressure supply enable state is maintained even if the current is stopped.
In the above-described composition, if the friction element (C-2) which engages during the time of high speed (4, 5, 6 speed) is once engaged, hydraulic pressure supply state is maintained by the hydraulic pressure to be supplied to the hydraulic servo (82), which operates the friction element (C-2), and supply of hydraulic pressure for the friction element (C-2) is not cut off and high speed is achieved without fail, even when failure occurs during high speed driving, stopping electric current to the signal pressure generation means. Furthermore, even if a failure occurs during low speed driving, stopping the electric current to the signal pressure generation means, the switching valve assumes the position to cut off supply of hydraulic pressure to the friction element, hence the low speed is achieved without fail.
In various other exemplary aspects, the control apparatus further comprises the third friction element (B-1, C-3) and a third control means (74, 73) for controlling the engagement and release by supplying and removing hydraulic pressure to the hydraulic servo (83, 84), which operates the third friction element, when the first control means (72) and the second control means (71) output hydraulic pressure, condition changes from engagement of the first friction element (C-2) and the second friction element (C-1) to the third control means (74, 73) ready to output hydraulic pressure, enabling supply of hydraulic pressure to the hydraulic servo (84, 83), the forward speed (4 speed) differing from the predetermined forward speed (5, 6 speed) is further achieved, and the second friction element (C-1) to be released with hydraulic pressure, as signal pressure, to the hydraulic servo (82) which operates the first friction element (C-2) achieves forward speed differing from the predetermined forward speed by releasing the third friction element (B-1, C-3) with hydraulic pressure, as signal pressure, to the hydraulic servo (81) which operates the second friction element at a different time of forward speed (4 speed) than the predetermined forward speed (5, 6 speed).
Moreover, some vehicles are structured in such a manner that when a failure occurs during driving of a vehicle, the forward speed is maintained by providing a valve which mechanically cuts off supply of hydraulic pressure to the friction element to be released with hydraulic pressure, as signal pressure, to the friction element engaged during each forward speed, in order to maintain forward speed at the time of failure, and by mechanically cutting off even if condition arises in which the control means to operate friction element to be released outputs hydraulic pressure due to electrical failure and the like, but a problem with such circuit is that when a failure occurs during driving and when subsequent stopping of vehicle causes turning off of the engine, release condition occurs due to removal of hydraulic pressure to each friction element. When the range is switched in order to start the vehicle by turning on the engine, because of the failure which occurred during driving, all the control means which operate each friction element output hydraulic pressure, causing all the friction elements to be in hydraulic pressure supply enable condition. In such a case, the circuit of above structure creates a problem in which, if a different forward speed (4 speed) is achieved by mechanically cutting off of hydraulic pressure supply to the friction element (B-1) to be released with a different forward speed (5, 6 speed) from predetermined forward speed with hydraulic pressure, as signal pressure, to the friction element (C-1) which is to be released with hydraulic pressure, as signal pressure, to predetermined friction element with predetermined forward speed (5, 6 speed), either forward speed to be established by the supply speed of the hydraulic pressure for friction element to be applied to the plurality of valves as signal pressure changes, or forward speed is not established due to occurrence of valve hunting. However, the problem of valve hunting is eliminated by compulsory preventing occurrence of one of two signal pressure regardless of speed of hydraulic pressure supply, hence, predetermined forward speed is established without fail. Here, instead of creating such structure, switching of hydraulic supply enable of cut off condition of the friction element (C-2) is achieved with hydraulic pressure to certain friction element, the hydraulic pressure speed to the friction element (C-2) changes due to hydraulic supply speed to the certain friction element.
In other various exemplary aspects, the control apparatus further comprises a fifth valve (69) for switching hydraulic pressure supply or cut-off to the hydraulic servo (83) which operates the fourth friction element (C-3) to be engaged during the time of the third forward speed (3 speed) with hydraulic pressure, as signal pressure, for the hydraulic servo (84) which operates the friction element (B-1) to be engaged during the time of the predetermined forward speed (2, 6 speed), a sixth valve (68) for switching hydraulic pressure supply or cut-off to the hydraulic servo (84) which operates the friction element to be engaged during the time of the predetermined forward speed (3 speed) with hydraulic pressure, as signal pressure, for the hydraulic servo (83) which operates the fiction element to be engaged during the time of the third forward speed (3 speed), and a seventh valve (66, 67) for switching hydraulic pressure supply or cut-off to the friction element which is to be engaged during the time of the predetermined forward speed or the fourth friction element with hydraulic pressure, as signal pressure (SLC 3, SLB 1), for the fourth friction element (C-3) or the friction element (B-1) to be engaged during predetermined forward speed time.
In the above-described composition, interlocking of the friction element (B-1) which engages at the time of predetermined forward speed and the friction element (C-3) which engages at the time of the third forward speed is prevented without fail by switching of the fifth through seventh valves.
In various other exemplary aspects, the control apparatus further comprises an eighth valve (66) capable of selective supply or cut-off of signal pressure to the sixth valve (68), and application of signal pressure to the sixth valve (68) and the seventh valve (67) is cut-off by applying to the eighth valve, as signal pressure, hydraulic pressure for the hydraulic servo (84) which operates the friction element (B-1) to be engaged during the predetermined forward speed time and hydraulic pressure for the first hydraulic servo (82) which is operated by the signal pressure generation means (SOL 1).
In the above-described composition, hydraulic pressure is not supplied to the first hydraulic servo (82) during re-starting. Hence, the eighth valve does not operate, resulting in release of the friction element (B-1) which is engaged during the time of predetermined forward speed (6 speed) due to cutting off of the sixth valve, enabling engagement of the third friction element (C-3).
In various other exemplary aspects, the control apparatus further comprises a ninth valve (67) capable of selective supply or cut-off of signal pressure to the fifth valve (69), and application of signal pressure to the fifth valve (69) and the seventh valve (66) is cut-off by applying to the ninth valve (67) hydraulic pressure for the hydraulic servo (83) which operates the fourth friction element (C-3).
In the above-described composition, hydraulic pressure is not supplied to the fourth hydraulic servo (83) during re-starting, hence, the eighth valve does not operate, resulting in release of the friction element (C-1) which is engaged during the time of third forward speed (3 speed) due to cutting off of the fifth valve, enabling engagement of the friction element (B-1) which is engaged during the time of predetermined forward speed.
In various other exemplary aspects, the control means comprises a pressure adjustment valve and a solenoid valve which enables, by applying signal pressure to the pressure adjustment valve, supply of hydraulic pressure from the pressure adjustment valve to the hydraulic servo which operates the friction element, and the hydraulic pressure for the hydraulic servo which operates the friction element to be applied to the fifth valve (69) and the sixth valve (68) is the hydraulic pressure from the solenoid valve.
In the above-described composition, tie-up of both friction elements is prevented when occurrence of a failure during the second forward speed (2 speed) enables the third forward speed, namely, when the friction element (C-3) is engaged by releasing the friction element (B-1).